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by David Canner
The X-ray structure of HIV-1 protease reveals that it is composed of two symmetrically related subunits which form a tunnel where they meet. This is critical because it contains the active site of the protease, consisting on two Asp-Thr-Gly conserved sequences, making it a member of the aspartyl protease family. The two catalytic Asp's either interact with the incoming water or protonate the carbonyl to make the carbon more electrophilic for the incoming water.

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by Alice Clark (PDBe)
In the 1970s, an exciting discovery of a family of medicines was made by the Japanese scientist Satoshi Ōmura. One of these molecules, ivermectin, is shown in this artwork bound in the ligand binding pocket of the Farnesoid X receptor, a protein which helps regulate cholesterol in humans. This structure showed that ivermectin induced transcriptional activity of FXR and could be used to regulate metabolism.

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Y Gu, V Srikanth, AI Salazar-Morales, R Jain, JP O'Brien, SM Yi, RK Soni, FA Samatey, SE Yalcin, NS Malvankar. Nature 2021 doi: 10.1038/s41586-021-03857-w
Geobacter pili were long thought to be electrically conductive protein nanowires composed of PilA-N. Nanowires are crucial to the energy metabolism of bacteria flourishing in oxygen-deprived environments. To everyone's surprise, in 2019, the long-studied nanowires were found to be linear polymers of multi-heme cytochromes, not pili. The first cryo-EM structure of pili (2021) reveals a filament made of dimers of PilA-N and PilA-C, shown. Electrical conductivity of pili is much lower than that of cytochrome nanowires. Evidence suggests that PilA-NC filaments are periplasmic pseudopili crucial for exporting cytochrome nanowires onto the cell surface, rather than the pili serving as nanowires themselves.

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J Prilusky, E Hodis doi: 10.14576/431679.1869588
This tutorial is designed for high school and beginning college students. When we breathe oxygen from the air is taken up by blood in our lungs and soon delivered to each of the cells in our body through our circulatory system. Among other uses, our cells use oxygen as the final electron acceptor in a process called aerobic respiration – a process that converts the energy in food and nutrients into a form of energy that the cell can readily use (molecules of ATP, adenosine triphosphate).

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